It is the long range purpose of this project to study interactions and relationships between connective tissue macromolecules as a way to understand connective tissue formation and structure. The topics of present interest are: 1) The mechanism of collagen fibril formation in vitro. 2) The effect of noncollagenous molecules on collagen assembly in vitro. We have developed a reproducible in vitro assembly system and shown that Type I collagen from rat tail tendon assembles in a multistep process. Studies are being extended to lathyritic Type I collagen from rat skin and type II collagen from rat chondrosarcoma.